1. Field of the Invention
This invention relates to time multiplexed systems and, more particularly, to an electron beam tube by which time multiplexing of an extremely high frequency carrier may be carried out.
2. The Prior Art
Time multiplexing of multichannel transmissions is a well known technique for combining the intelligence of a plurality of separate channels on a single carrier. Such systems are described, for example, in "Taschenbuch der Hochfrequenztechnik" by Meinke and Gundlach, 1956. In one method described therein, a plurality of individual channels are scanned by a revolving electronic switch or commutator, to give a train of pulses having amplitudes during successive time periods corresponding to individual channel signals. A carrier is then modulated with the pulse train by a modulator and transmitted to a receiver, where the signal is received and passed through a demodulator, and the resulting signal is demultiplexed into individual channels by means of a distributor which is synchronized with the commutator of the transmitter.
When the intelligence to be transmitted on the individual channels comprises binary signals, the carrier modulation employed is preferably phase shift keying two-phase modulation, sometimes hereinafter referred to as "PSK modulation." In this modulation technique, the signals are scanned by a commutator which revolves at a constant frequency, and a carrier wave is then phase modulated in such a way that signals representative of the binary 1 correspond to one phase and signals corresponding to a binary 0 correspond to another phase, shifted 180.degree., for example, relative to the first phase.
PSK modulation has been practical heretofore only with relatively low frequency carriers, and it has not heretofore been possible to utilize such a method with an extremely high frequency carrier such as 50 GHz or the like. The prior art has not been able to develop a sufficiently fast electronic switch which can be synchronized at the transmitter and receiver locations. If a 50 GHz carrier could be used, it would be possible to multiplex 16 channels of binary information, each having a pulse repetition rate of 250 MHz, by using an electronic switch operating at 250 MHz, producing a multiplexed signal of 4 GHz for phase modulating the carrier.
It is therefore desirable to provide a system by which PSK modulation may be applied to an extremely high frequency carrier in the range of 50 GHz.